Multi-short-scan technique in SPECT imaging

ABSTRACT

A SPECT system which scans over multiple separate scans and individually motion compensates the information obtained from each of these scans. The separate scans may be over different angular extents and may be for different purposes. One of the scans for example may be a scout scan, and the other scans may then be scans which concentrate on areas identified during the scout scan. Alternatively, the scans may all being exactly the same and stitched together after the individual motion compensation. Since each of the scans are shorter, the patient will presumably have moved less during each individual scan, and the amount of motion is hence presumably less.

This application claims priority from Provisional application No.60/865,914, filed Nov. 15, 2006, the disclosure of which is herewithincorporated by reference herein.

BACKGROUND

In SPECT imaging, data acquisition is usually completed in a singlescan. A scan usually obtains between 30 and 128 projection frames areacquired in a 180° to 360° angular range, depending upon the clinicalprotocols. SPECT often has a low count rate because of low systemsensitivity and patient dose compared to other imaging modalities, suchas CT. The SPECT scan hence takes a relatively long time, e.g., fromminutes to tens of minutes. Theoretically, SPECT imaging requires thepatient to stay motionless during the entire scan. Any movement by thepatient causes data inconsistency which may introduce motion artifactsinto the final images.

However, it is very difficult to keep patients motionless during scans,and especially during long scans. When the patient motion becomes toolarge, the data may not be medically usable. Patients are generallyrescanned when this happens.

For example, for cardiac SPECT, ASNC guidelines specifically requiresthat if patient motion is larger than a certain amount at any of theprojection frames, the patients need to be rescanned.

Wang et al (Wang et al 2005) used multiple acquisition of moderatelength to reduce effects of radioactive decay for phantom experiments.Chen et al (Chen et al 2004) used multiple sequential scans (fastfanning) with 1 second per projection for dynamic SPECT usingTeboroxime. However, neither of these works could be directly used tohandle motion correction in SPECT imaging.

A number of motion correction techniques have been proposed for SPECTimaging. These efforts can be divided into two main categories. One is ahardware approach that tracks patient motion during patient scans usinga tracking device and uses the motion information during imagereconstruction to correct for the motion. The other analyzes theacquired data after the scan using software, where the data are acquiredusing the current single but relatively long scan approach.

The hardware approach is ideal for motion tracking and correction forpatient studies, but the device can be complicated and expensive.

The software approaches are limited in their ability to correct forsub-frame patient motion. For example, if the scanning time for oneframe is 20 seconds, and the patient moves only for the second half (10seconds) of the acquisition of the frame, unless the data are acquiredin list mode, none of the current motion correction techniques willoperate properly.

SUMMARY

According to embodiments, a single photon image computed tomography scanis carried out to obtain multiple separate scans, each representing amedical image at least one portion of a body being imaged. According toan embodiment, the total amount of desired counts from the patients areobtained over multiple shorter scans as compared with over a singlescan.

One embodiment may use two separate scans to obtain the total number ofcounts from the patient. Another embodiment may use four shorter scansor some other number of scans.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures:

FIG. 1 illustrates how the multiple short scans can reduce the motion ineach of the short scan data;

FIG. 2 illustrates multiple short scans that can reveal differentoverlying tissue attenuation effects;

FIG. 3 illustrates an application of a scout scan technique.

DETAILED DESCRIPTION

In clinical studies, patient motion is in general small and gradual. Itis very difficult or impossible to determine the amount and direction ofthe movement without a real-time motion tracking device that provideson-the-fly information of patient motion. Most clinical SPECT systemslack such motion tracking devices. Hence, only after the scan iscompleted can one check if the patient has moved in the scan, and howmuch. If the motion is above the acceptable value, the patient thenneeds to be rescanned.

In practice, rescanning a patient has many disadvantages. One is theextra scanning time that is taken by the rescan, which results inlowered patient throughput and less certainty in the ability to scheduleothers. Another is the change of patient physiology andradiopharmaceutical distribution with time. Some radiopharmaceuticaldistributions change significantly with time, such as those with veryshort physiological half time or those which redistribute quickly in theorgan/tissue of interest. With those agents, rescanning the patient mayrequire the re-preparation of the patient, re-dose, re-exercise, etc, oreven rescheduling of the patient. Also, since the fees for these medicalprocedures are in general capped by insurance, it may not be possible tocharge any extra for a re-scan.

This disclosure describes a multi-short-scan technique in SPECT imagingas an alternative to the current single, relatively long scan approachfor patient studies. This technique can be used to correct patientmotion and reduce the chance of patient rescans.

The inventor recognized, however, that several short scans have lessoverall motion in each of the short scans than a single long scan andallows for better motion correction. FIG. 1 illustrates a motionscenario. In FIG. 1, the line 105 shows the motion contained in theacquired data of a patient during a scan when a single scan is used. Incontrast, the lines 110, 111 112, 113 show the motion contained in thedata acquired using four separated and short scans. The patient motionsmay be better compensated during short scans than they are during alonger scan.

Instead of a single long scan for patient studies, this disclosuredescribes the use of multiple short scans, e.g., between 2 and 32 shortscans. The short scans can be acquired with the same effective geometryor with different geometries for one or all of the short scans. When thesame geometry is used, the scanning may scan from beginning to end ofthe geometry, and return back from end to beginning. This may continueuntil the desired number of photon counts are received. This multiplescan system may allow (1) better motion correction, (2) identificationof overlying tissue attenuation, and (3) better identification of regionof interest to be scanned.

Patient motion in SPECT imaging can be gradual (such as slumping) orabrupt (such as coughing), or a combination of the two. When a single,long scan is used, the data is deteriorated by the overall motion duringthe whole scan. However, if multiple short scans are used, the data ofeach short scan is only deteriorated by the motion during that shortscan. The motion during the short scans can be much smaller than themotion in the single, long scan. Hence, there is typically less datainconsistency over the course of the short scan. There is also theability for a usually better motion correction using software for themotion in each of the short scans. Thus, the image of each of the shortscans can be more accurate, i.e. have fewer motion artifacts than theimage of the single, long acquisition.

Even though the multiple short scans will inherently have less motiontherein than the longer time scans, the data from each of multiple shortscans can still be individually motion-corrected.

If each short scan acquires data at exactly the same geometry, the datafrom the multiple short scans is subsequently added together for imagereconstruction. Some simple registration is used for the adding process.

If the multiple short scans do not acquire data at exactly the samegeometry, then one can reconstruct the image for each of the multipleshort scans, and later apply some simple registration to add up thereconstructed images of each of the short scans to obtain the finalimage.

Another unexpected advantage comes from using multiple short scansinstead of a single long scan. Specifically, if the multiple short scansacquire data in different angular ranges, then the reconstructed imageof each of the multiple short scans may reveal different overlyingtissue attenuation which may assist with the clinical interpretation ofthe images.

When multiple short scans are used, one can also reconstruct the imageafter each short scan. The first short scan is used to cover a largeangular range, and is used as something similar to the “scout view” inCT imaging. Reconstruction from this “scout scan” data can help toidentify regions that should receive the most scanning attention fromthe rest of the scans.

Using multiple short scans may allow for better motion correction forclinical applications than using a single long scan. Moreover, it mayallow the short scans to cover different angular ranges so that they canreveal different imaging effects, such as overlying tissue attenuation.The “scout scan” scan together with other short scans will allow theidentification of the region to be scanned and better usage of cameratime by allowing improved sensitivity for the region of interest.

Another embodiment may use these techniques for cardiac SPECT imaging,where imaging time is relatively long and overlying tissue attenuationis critical for clinical interpretation. The techniques disclosed hereincan also be used for SPECT oncology.

In SPECT oncology, a “scout scan”: a short scan image shows differentlesions. This image allows the identification of some lesions that areclear and some that are unclear, or some as benign or malignant butothers are ambiguous (through SUV values). Using the scout scan image,one can dedicate the rest of the short scans to the regions wherelesions are unclear or the physiological stage of the lesion isambiguous.

FIG. 2 also shows the scanning camera 199 which may be a sensor of thetype used for suspect detection. FIG. 2 shows the camera in a locationwhere it can be scanned, and also shows how the camera can be moved to asecond location 198 which scans over a different path. Alternatively,however, the patient can be moved to that different location, so thatthe patient's movement changes rather than the camera's movement.

FIG. 2 illustrates how multiple short scans can cover different angularranges. For example, a first short scan 200 may cover a first angularrange, while a second short scan 205 may cover a second angular range.Both of these ranges should ideally include the organ of interest 210,as well as other image items such as 215.

FIG. 3 illustrates how a scout scan could be used. In this scout scan,different lesions can be identified. Some regions may be identifiable,such as 300, which is clearly identifiable as malignant, but otherregions may be unclear, such as the region 305. Some may be completelyclearly benign such as 310. Others, through use of the SUV values, maybe ambiguous 315. The initial short scan can be used as a scout scan,followed by other scans being used to identify, followed by other scansbeing used to scan the unclear regions.

Mechanical devices and software can be used to rotate the camerarelative to the patient according to the application of the embodiments,e.g., as shown in FIGS. 2 and 3 which shows relative rotation betweenthe camera and patient. The mechanical devices and software can be usedto minimize the time used for camera reconfiguration between the shortscans. Alternatively, the patient can be rotated relative to the camera.The patient can be rotated back and forth, for example, until thedesired number of scans are obtained.

The general structure and techniques, and more specific embodimentswhich can be used to effect different ways of carrying out the moregeneral goals are described herein.

Although only a few embodiments have been disclosed in detail above,other embodiments are possible and the inventors intend these to beencompassed within this specification. The specification describesspecific examples to accomplish a more general goal that may beaccomplished in another way. This disclosure is intended to beexemplary, and the claims are intended to cover any modification oralternative which might be predictable to a person having ordinary skillin the art. For example, other kinds of medical imaging systems could beused with this embodiment. Other differences between the scans could beused. Other compensations can be applied to the scans.

Also, the inventors intend that only those claims which use the words“means for” are intended to be interpreted under 35 USC 112, sixthparagraph. Moreover, no limitations from the specification are intendedto be read into any claims, unless those limitations are expresslyincluded in the claims. The computers described herein may be any kindof computer, either general purpose, or some specific purpose computersuch as a workstation. The computer may be an Intel (e.g., Pentium orCore 2 duo) or AMD based computer, running Windows XP or Linux, or maybe a Macintosh computer. The computer may also be a handheld computer,such as a PDA, cellphone, or laptop.

The programs may be written in C or Python, or Java, Brew or any otherprogramming language. The programs may be resident on a storage medium,e.g., magnetic or optical, e.g. the computer hard drive, a removabledisk or media such as a memory stick or SD media, wired or wirelessnetwork based or Bluetooth based Network Attached Storage (NAS), orother removable medium or other removable medium. The programs may alsobe run over a network, for example, with a server or other machinesending signals to the local machine, which allows the local machine tocarry out the operations described herein.

Where a specified logical sense is used, the opposite logical sense isalso intended to be encompassed.

1. A computer program product, comprising a computer usable mediumhaving a computer readable program code embodied therein, said computerreadable program code adapted to be executed to operate a single photonemission scanning device, that has at least one single photon emissioncamera; and a scanning part, that moves at least one of said camerarelative to a body being scanned or said body relative to said camera;said computer program product operative to: receive information from thescan; control said scanning part to scan information from the body beingscanned over a plurality of separate scans, each of said separate scansreceiving only a portion of the total number of total counts that aredesired, said control comprising a control to scan first over an area ofa scout scan, and then processes said scout scan to determine regions ofinterest, and then controls said scanning part to scan said regions ofinterest determined during said processes of said scout scanpreferentially to other regions; receive information from each saidscan; motion compensate a first scan to compensate for patient motionduring said first scan, and separately motion compensating a second scanto compensate for patient motion during said second scan.
 2. A productas in claim 1, wherein said computer product is operative to move thescanning part to cause the scanning part to scan over a differentangular range during said first scan than said second scan.
 3. A productas in claim 1, wherein said computer product is operative to controlsaid scanning device to scan multiple times after said scout scan, andto individually motion compensate each of plural scans after said scoutscan.
 4. A product as in claim 1, wherein said computer product isoperative to control said scanning device to scan over at least fourdifferent scans and to individually motion compensate each of said atleast four different scans.
 5. A method, comprising: obtaining multipledifferent single photon emission images over multiple different scansincluding at least a first scan and a second scan; motion compensatinginformation obtained during said first scan to obtain first motioncompensated information about the first scan; separately motioncompensating information obtained during said second scan to obtainsecond motion compensation information about the second scan; and usingboth said first scan and said second scan to obtain a combined imageindicative of medical imaging of the multiple different scans, whereinsaid first scan is a scout scan that scans an entire area being imaged,and further comprising monitoring results of said scout scan todetermine areas of interest, and wherein said second scan concentratesmore on said areas of image interest then on other areas.
 6. A method,comprising: obtaining multiple different single photon emission imagesover multiple different scans including at least a first scan and asecond scan; motion compensating information obtained during said firstscan to obtain first motion compensated information about the firstscan; separately motion compensating information obtained during saidsecond scan to obtain second motion compensation information about thesecond scan; and using both said first scan and said second scan toobtain a combined image indicative of medical imaging of the multipledifferent scans, wherein said first scan is processed for a firstpurpose and said second scan is processed for a second purpose differentthan said first purpose.
 7. A method as in claim 6, wherein said firstscan is over a first angular range and said second scan is over a secondangular range different the first angular range.